The present invention relates to methods and devices for monitoring the functions of a display system which receives data from any data-producing unit connected thereto.
Display systems of measuring instruments such as, for example, weight scales which are used to weigh commercial vehicles and the loads carried by such vehicles, are subject to compulsory calibration. Such calibration is generally legally standardized, which imposes high demands on the functional reliability of the scale. Failures or changes in the operating characteristics of components in such a display system which has no means for error recognition result in inaccurate displays. The reliability of the particular measuring instrument depends upon the frequency of such faulty displays. Circuits which are generally disposed between a means for determining the measured value and the display system, which circuits not only transmit the measured values but also store those values, are becoming increasingly complex and devices for monitoring the operation of such circuits are becoming correspondingly complex. This is particularly so if a microprocessor is employed as a data compiling and generating unit.
Semiconductor modules are known which accept a complete data record from a microprocessor system and independently drive a display system comprising several decades in multiplex operation. Because the microprocessor and the internal multiplexer of the display system are generally asynchronously operated, it is not possible to check the operation of the display system for errors without auxiliary means.
It is thus an object of the present invention to provide a method and apparatus for monitoring the functions of a display system which is simple in operation and can be economically employed in conjunction with systems utilizing a microprocessor. The above object is inventively achieved in a method and apparatus which display data which is accepted from a microprocessor, which store the displayed data, and which check the stored displayed data for identity with the data which is to be accepted and to be displayed. In this manner, a check can be undertaken not only to determine whether the circuit of the display system accepting the data has properly accepted the data, but also checks for malfunctions in the display system itself, such as the existence of short circuits or open circuits within a display unit. Such malfunctions can be immediately detected because the stored data will correspond to the data intended for display only when no errors occur either in the display system or in the circuit accepting the data, thus insuring the accuracy of the displayed data.
In a further embodiment of the invention, the identity check is undertaken decade by decade. This affords the ability of topically tracing an existing error such as, for example, the failure of a particular component.